A friend of mine is using my 2003 Ford Transit Luton van , its a factory fitted version .
He has driven through France and northern Spain with a high idle and a refusal of the van to stay running on gas we have changed the idle control valve which only made things worse .
I have asked him to check and if possible replace all vacuum pipes
put old idle control valve back but well lubricated first and make sure there are no air leaks
Clean the sensors on the Vaporisor and also the filter ( if we can find one )
Spray around the intake manifold with WD40 to check for air leaks
Thats about the limit of what we can do, any help or hints would be appriciated or anything obvious i have forgotton

Theres two versions of the Necam systems - its a fair bet it will be one of them, If its been working and then suddenly fails to run on gas it suggests either your exhaust sensor is playing up or dead (should be able to monitor if it works on petrol using obd to see that) or the vapouriser is failing to keep a constant supply of pressure.

If nothing has been done on the van recently the vapouriser would be my first place to look - Easy check first to see if its a leaking diaphragm is to remove the vacuum line from it and check if gas is being leaked into the manifold that way. Some water in a jar over the open end of the hose would prove or disprove that.

Any idea if its the EGi type or GSI type (EGI has the distributor, GSI injectors)

without Guessing I do not know which system it has , it has a vaporisor that feeds the gas to the injectors I believe that was the main one fitted to the MK6 transits .
With the high idle I was not sure if this could be related to the mysterious rpm filter that I have heard so much about ?

The RPM filters do fail - Typically the lights on the display will give a clue whats happening. If it has injectors its the GSI system if its the Necam or Koltec equipment fitted.

The description of the RPM filter doesn't make it very clear what it is - its a PCB with a few components, not really a filter more an amplifier and emulator for the lambda signal - Looks like this if you haven't already found one https://www.autogasshop.co.uk/necam-for ... -442-p.asp It may be near the LPG ecu, I've not seen the van install to know how its done on them although afaik is is the same front end kit as the cars use.

It may be that failed, best way to tell is swap it for a known good one. Any idea what the lights do when it fails/Plays up? Any Fault codes logged by the petrol system? Probably won't be anything from the lpg side as it does attempt to switch over so doubt its detecting anything wrong.

If your mate can find the vacuum line from the vapouriser its worth checking that, as given the age of the system its likely the vapouriser is in need of attention particularly if it hasn't had much.

Slowly catching up with threads I've missed due to being so busy installing and fixing LPG systems.

Adding to Bri's suggestions...

Most likely EGI. High idle suggests too rich (too much LPG) at idle.

Not clear if either 1. the van refuses to run on gas under load completely or 2. it will run on gas under load but still switches back to petrol.
Most Koltec systems including those on Transits monitor mixture via lambda and if mixture hangs rich or lean for too long they will 'time out' and switch back to petrol with the switch flashing to indicate there's a problem. A faulty reducer, gas distributor (EGI), injectors (GSI) or lambda probe could all cause the van to give the symptoms you're seeing (will run on gas but only under certain conditions / only for a while). Without having a proper look, 1 is more likely to be due to a faulty fuel distributor unit than problem reducer. 2 could be either but more likely faulty reducer. Seems the RPM filter and petrol injector relays are working or it wouldn't idle on 4 cylinders on gas, you can check lambda operation via a normal OBD2 live data scanner when running on petrol.